Patent Document 1: JP-A 2007-111635
Patent Document 2: JP-A 2006-228450
Patent Document 3: JP-A 2005-306706
Patent Document 4: JP-A 2006-83050
Generally, various electrode catalysts used in fuel cells or the like are obtained in the form of composite particles such as those of metal-supported carbon having metal particles supported on the surface of a solid carrier, obtained by supporting a metal component on the surface of an electroconductive carrier such as carbon by impregnation, ion-exchange, co-precipitation or the like in an aqueous solution of a metal salt or in a colloidal dispersion system. Among these electrode catalysts, those metal catalysts using metals particularly noble metals have been used, but the noble metal elements occur in limited amounts on earth, and thus it is necessary that their used amounts be reduced as much as possible and their action as the catalyst be improved as much as possible. As metal catalysts, therefore, those with a structure having metal microparticles supported on the surfaces of carrier particles consisting of carbon black, inorganic compounds or the like are used. Their activity varies depending not only on the type of metal but also on the size of supported metal microparticles, the type of crystal face, the type of carrier and the like, among which the shape and size of metal microparticles can be mentioned as major factors influencing the activity, and regulation thereof is particularly important.
As the method of efficiently obtaining a metal-supported catalyst, use has been made of a method wherein the surface of a carbon carrier is subjected to oxidation treatment and a metal is supported on the surface thereof by a liquid-phase reduction method, thereby forming metal-supported carbon (JP-A 2007-111635/Patent Document 1) and a method of using two kinds of nonionic surfactants or a combination of one kind of nonionic surfactant and one kind of ionic surfactant (JP-A 2006-228450/Patent Document 2).
Meanwhile, crystals consisting of fullerene molecules, and fullerene nanowhiskers/nanofiber nanotubes, have been produced by various methods (Patent Documents 3 and 4).
For example, a method wherein a solution containing a first solvent having fullerene dissolved therein is combined with a second solvent in which fullerene is less soluble than in the first solvent, to form a liquid-liquid interface between the solution and the second solvent, thereby precipitating carbon thin lines in the liquid-liquid interface, is known (Patent Document 3).
However, when the actual reaction in the method of obtaining metal-supported catalysts is carried out in a test tube or a beaker or in a tank as manufacturing technique, the raw materials are actually hardly uniformly reacted due to uneven mixing of the raw materials and the temperature-distribution unevenness accompanying the uneven mixing, thus resulting in yield drop, deficient or uneven amounts of supported catalysts, and larger sizes of supported metal particles than intended. As a consequence, the amount of production has been reduced.
In these methods, there is a limit to the effect of reducing the particle sizes of metal microparticles, but if the efficiency of the catalyst could be improved by further reducing the particle sizes of the metal microparticles, the characteristics of a fuel cell for example could further be improved, for which a new production method has been demanded.
With regard to fullerene, crystals consisting of fullerene molecules and fullerene nanowhisker/nanofiber nanotubes can be formed by the methods described above, but the reaction conditions are not uniform, so that products having or not having a hollow structure in crystals have been formed. When a metal is supported or included by these methods, a desired substance is hardly uniformly obtainable because of difficult control of liquid-liquid interface, thus making these methods less suitable for mass production.
As shown in, for example, Patent Document 4, it has been attempted to use a microreactor or a micromixer, known as microchemical process, in the manufacturing steps of forming and supporting the slight metal microparticles, but when the metal microparticles are formed and supported by these methods, a micro-flow-path may with high possibility be clogged with products or with foams or byproducts generated by the reaction, and moreover the reaction will proceed basically through only diffusion of molecules, and therefore, these methods are not applicable to every reaction. The microchemical process uses a scale-up method of increasing the number of reactors arranged in parallel, but there is a problem that because the manufacturing ability of one reactor is small, large scale up is not practical, and the respective reactors are hardly endowed with the same performance, thus failing to provide uniform products. When the reaction solution is highly viscous or the reaction causes an increase in viscosity, very high pressure is necessary for passage of the solution through a minute flow path, so there is a problem that a usable pump is limited, and leakage of the solution from an apparatus cannot be solved due to application of high pressure.